Method and apparatus for determining the rotational rate of a rotating device

Abstract

A non-invasive apparatus and method for measuring the speed of a rotating device that includes a sensor that measures a dynamic characteristic of the rotating device. A sample of the signal is transformed from the time domain into a frequency spectrum. The frequency spectrum is then analyzed to determine the motor speed. The resulting motor speed can be combined with other motor data by an order analysis to identify malfunctioning or improperly installed components.

1. An apparatus for measuring the rate of rotation for a rotating device comprising of:
 a sensor that measures a time varying parameter of the rotating device, said sensor being operative to generate a signal that is proportional to the measured rotating device parameter;  
 a dynamic signal analysis device connected to said sensor, said dynamic signal analysis device operative to sample said signal generated by said sensor, said signal analysis device further operative to digitize said signal generated by said sensor; and  
 a signal processing device connected to said dynamic signal analysis device, said signal processing device operative to transform said sampled and digitized sensor signal from a time-domain signal into a frequency domain spectrum, said signal processing device further operative to analyze said frequency domain spectrum to determine the rotation rate of the rotating device.  
 
   
   
     2. The apparatus according to  claim 1  wherein said signal processing device is a microcomputer. 
   
   
     3. The apparatus according to  claim 1  wherein said signal processing device is included in an application specific integrated circuit. 
   
   
     4. The apparatus according to  claim 1  wherein said signal processing device is a digital signal processor chip. 
   
   
     5. The apparatus according to  claim 1  wherein said signal processing device is a digital computer. 
   
   
     6. The apparatus according to  claim 1  wherein said transform is a Fast Fourier Transform. 
   
   
     7. The apparatus according to  claim 1  wherein said transform is a Discrete Fast Fourier Transform. 
   
   
     8. The apparatus according to  claim 6  wherein the rotating device is an electric motor and the time varying parameter is the motor current and further wherein said signal processing device is operative to determine the motor speed from the following formula:
     f   1 =[(motor speed)(number of motor poles)(number of motor phases)]/60,  
 where f 1  is a first maximum of the frequency spectrum above a minimum frequency.  
 
   
   
     9. The apparatus according to  claim 6  wherein the rotating device is a gear pump and the time varying parameter is the time varying pressure produced by the pump and further wherein said signal processing device is operative to determine the motor speed from the following formula:
     f   1 =[(motor speed)(number of gear teeth)]/60,  
 where f 1  is a first maximum of the frequency spectrum above a minimum frequency.  
 
   
   
     10. The apparatus according to  claim 6  wherein said rotating device is an electric motor and further wherein said signal processing device further is operative to perform an N th  order frequency analysis that determines the motor speed from the following formula:
     rpm =( f   N )(60)/(number of poles)(number of phased)( N )=( f   N )(0.535),  
 where: 
     f   N ={maximum value within the range of (4 f   1 −5 bins)< f   4 <(4 f   1 +5 bins)}.  
 
 
   
   
     11. The apparatus according to  claim 6  wherein said rotating device is an electric motor and further wherein said motor is adapted for use in a vehicle electrically powered hydraulic steering system. 
   
   
     12. The apparatus according to  claim 11  further including a load connected to the shaft of said motor, said load providing a time varying loading that simulates operation of an electrically powered hydraulic steering system. 
   
   
     13. The apparatus according to  claim 11  further including a hydraulic pump connected to said motor, said hydraulic pump connected to a hydraulic load that is operative to simulate operation of an electrically powered hydraulic steering system. 
   
   
     14. The apparatus according to clam  13  wherein the electric motor includes at least one conductor for supplying electricity to the motor and further wherein said sensor is a current probe that is adapted to be clamped over said conductor, said current probe being operative to generate a signal that is proportional to a current flowing in said conductor. 
   
   
     15. The apparatus according to  claim 13  wherein said sensor is a first sensor and further wherein the apparatus includes a second sensor adapted to be attached to said motor, said second sensor generating a sensor signal that is representative of the operation of said motor, said second sensor connected to said dynamic signal analysis device with said second sensor signal being sampled and digitized, said computer being operative to utilize said rotation rate of said motor to transform said second sensor signal to determine the condition of a motor component. 
   
   
     16. The apparatus according to  claim 15  wherein said motor sensor is an accelerometer and said sensor generates a signal that is representative of a motor vibration. 
   
   
     17. A method for measuring the rate of rotation for a rotating device, the method comprising the steps of:
 (a) providing a sensor that is connected through a dynamic signal analysis device to a signal processing device that includes an algorithm for transforming a time domain signal into a frequency spectrum;  
 (b) using the sensor to measure a dynamic characteristic of the rotating device, the sensor being operative to generate a signal that is proportional to the dynamic characteristic of the rotating device;  
 (c) varying a load applied to the rotating device;  
 (d) measuring the signal generated by the sensor during step (c);  
 (e) sampling and digitizing the measured signal with the dynamic signal analysis device;  
 (f) transforming the sampled and digitized signal into a frequency spectrum with the signal processing device algorithm; and  
 (g) determining a value for the rate of rotation for the rotating device from the frequency spectrum.  
 
   
   
     18. The method according to  claim 17  wherein the transformation in step (f) utilizes a Fast Fourier Transform. 
   
   
     19. The method according to  claim 17  wherein the transformation in step (f) utilizes a Discrete Fast Fourier Transform. 
   
   
     20. The method according to  claim 19  wherein the rotating device is an electric motor and the parameter is the current supplied to the motor. 
   
   
     21. The method according to  claim 20  wherein the sensor provided in step (a) is a current probe that is clamped over a conductor supplying an electric current to the motor with the probe being operable to in step (b) to generate a signal that is proportional to the current flowing through the conductor. 
   
   
     22. The method according to  claim 19  wherein the rotating device is a pump and the parameter is the time varying pressure produced by the pump. 
   
   
     23. The method according to  claim 20  wherein step (g) includes determining the motor speed from the following formula:
     f   1 =[(motor speed)(number of motor poles)(number of motor phases)]/60,  
 where f 1  is a first maximum of the frequency spectrum above a minimum frequency.  
 
   
   
     24. The method according to  claim 17  wherein the motor speed determination in step (g) further includes an N th  order frequency analysis. 
   
   
     25. The method according to  claim 24  wherein step (g) includes determining the motor speed from the following formula:
     rpm =( f   N )(60)/(number of poles)(number of phased)( N )=( f   N )(0.535),  
 where: 
     f   N ={maximum value within the range of (4 f   1 −5 bins)< f   4 <(4 f   1 +5 bins)}.  
 
 
   
   
     26. The method according to  claim 20  wherein the sensor is provided in step (a) is a first sensor and further wherein a second sensor is attached to said motor in step (b), said second sensor generating a signal in step (d) that is a function of a non-speed motor parameter, and further wherein step (g) includes using the motor speed and the sensor output to determine the condition of a motor component. 
   
   
     27. The method according to  claim 26  wherein the non-speed data is transformed to determine the condition to the motor component.